THE BEST OF GREEN DESIGN: In the United States, 56 percent of single-family homes are underinsulated, resulting in 800 trillion BTU of lost energy. Plant-based products efficiently stem the flow.

Surface temperatures on a flat, black roof can easily exceed 160 F on a sunny afternoon. The same roof covered in drought-tolerant plants will be as much as 100 degrees cooler -- dramatically reducing the cost of a/c. GreenGrid, a modular system of preplanted, recycled-plastic trays, presents a lightweight, low-cost alternative to permanent systems. In many cases, it can be installed atop existing roof gravels, residential or commercial.